Radiation-Induced Triggering for Set-On-Command Compositions and Methods of Use

ABSTRACT

Methods of isolating a portion of a wellbore comprising placing a sealant composition into a subterranean formation after drilling of the wellbore therein and subjecting the sealant composition to ionizing radiation wherein subjecting the sealant composition to the ionizing radiation alters the set modifier. The sealant composition comprises a set modifier selected from the group consisting of an accelerator, an oxidizing agent, a set retarder, and combinations thereof. And the sealant composition comprises a polymeric component.

FIELD OF THE INVENTION

The present invention generally relates to hydrocarbon exploration andproduction operations, such as subterranean cementing operations, andmore particularly to compositions and methods that allow for greatercontrol over the setting of fluids or slurries used during suchoperations.

BACKGROUND OF THE INVENTION

Natural resources such as oil and gas located in a subterraneanformation can be recovered by drilling a wellbore down to thesubterranean formation, typically while circulating a drilling fluid inthe wellbore. After the wellbore is drilled, a string of pipe, e.g.,casing, can be run in the wellbore. The drilling fluid is then usuallycirculated downwardly through the interior of the pipe and upwardlythrough the annulus between the exterior of the pipe and the walls ofthe wellbore, although other methodologies are known in the art.

Hydraulic cement compositions are commonly employed in the drilling,completion and repair of oil and gas wells. For example, hydrauliccement compositions are utilized in primary cementing operations wherebystrings of pipe such as casing or liners are cemented into wellbores. Inperforming primary cementing, a hydraulic cement composition is pumpedinto the annular space between the walls of a wellbore and the exteriorsurfaces of a pipe string disposed therein. The cement composition isallowed to set in the annular space, thus forming an annular sheath ofhardened substantially impermeable cement. This cement sheath physicallysupports and positions the pipe string relative to the walls of thewellbore and bonds the exterior surfaces of the pipe string to the wallsof the wellbore. The cement sheath prevents the unwanted migration offluids between zones or formations penetrated by the wellbore. Hydrauliccement compositions are also commonly used to plug lost circulation andother undesirable fluid inflow and outflow zones in wells, to plugcracks and holes in pipe strings cemented therein and to accomplishother required remedial well operations. After the cement is placedwithin the wellbore a period of time is needed for the cement to cureand obtain enough mechanical strength for drilling operations to resume.This down time is often referred to as “waiting-on-cement”, or WOC. Ifoperations are resumed prior to the cement obtaining sufficientmechanical strength, the structural integrity of the cement can becompromised.

Two common pumping methods have been used to place the cementcomposition in the annulus. The cement composition may be pumped downthe inner diameter of the casing and up through the annulus to itsdesired location. This is referred to as a conventional-circulationdirection method. Alternately, the cement composition may be pumpeddirectly down the annulus so as to displace well fluids present in theannulus by pushing them up into the inner diameter of the casing. Thisis referred to as a reverse-circulation direction method. Cement canalso be used within the wellbore in other ways, such as by placingcement within the wellbore at a desired location and lowering a casingstring into the cement. The latter method may be used, for example, whenthere is not the ability to circulate well fluids due to fluid loss intoa formation penetrated by the wellbore.

In carrying out primary cementing as well as remedial cementingoperations in wellbores, the cement compositions are often subjected tohigh temperatures, particularly when the cementing is carried out indeep subterranean zones. These high temperatures can shorten thethickening times of the cement compositions, meaning the setting of thecement takes place before the cement is adequately pumped into theannular space. Therefore, the use of set retarding additives in thecement compositions has been required. These additives extend thesetting times of the compositions so that adequate pumping time isprovided in which to place the cement into the desired location.

While a variety of cement set retarding additives have been developedand utilized, known additives, such as sugars or sugar acids, canproduce unpredictable results. Hydroxy carboxylic acids, such astartaric acid, gluconic acid and glucoheptonic acid are commonly used inoil well cementing as a cement retarder. However, if an excess ofhydroxy carboxylic acid is used it can over-retard the set of the cementslurry and thereby causing it to remain fluid for an extended period oftime. This over-retardation can result in extended waiting time prior toresuming drilling and may allow gas to invade the slurry thereby causingunwanted gas migration. The extended waiting time results in delays insubsequent drilling or completion activities.

In a number of cementing applications, aqueous salt has been utilized asan additive in cement compositions. The salt, generally sodium chloride,functions as a dispersant in cement slurry, causing the slurry to expandupon setting whereby the attainment of a good bond between the wellboreand casing upon setting of the slurry is enhanced. However, saltsaturated slurries can cause problems to bordering formations, and incertain situations salt can be leached out of the cement slurry, whichcould cause cement failure. Also, certain salts, such as calcium salts,can act as accelerating agents, which reduce the setting time of thecement composition in an attempt to overcome the negative effects of setretarders. However, the presence of a set and strength acceleratingagent, such as calcium salt, in the cement composition can increase therisk that the cement composition may thicken or set before placement.Given the complexity of the cement chemistry and the large temperatureand pressure gradients present in the wellbore, and the difficulty inpredicting the exact downhole temperatures during the placement andsetting of the cement, it can be difficult to control the retardingadditive and accelerating agent to get the desired setting behavior.Systems generally are over-engineered to have very long setting (orthickening) times in order to ensure that the mix remains fluid untilall of the cementitious material is in place which can result inexcessive WOC.

Therefore, there is a need for improved set control methods, which bringabout predictable cement composition setting times in the subterraneanenvironments encountered in wells. In particular, it is desirable todevelop methods for rapidly setting cement-based systems whereby thetiming of the setting is under the control of technicians in the fieldwithout the risk of premature setting. Thus, a need exists for a methodof cementing a wellbore that would simultaneously contain sufficientretarder material to ensure proper pumpability for the desired pumpingduration and a sufficient concentration of an accelerator to shorten thesetting time, whereby the thickening effect of the accelerator is underthe control of technicians in the field.

SUMMARY OF THE INVENTION

The present invention generally relates to wellbore fluid and/or slurrycompositions that allow for greater control over the setting of suchcompositions in a wellbore.

Disclosed herein is a method of isolating a portion of a wellbore bypreparing a sealant composition comprising a set modifier component. Thesealant composition is placed into a wellbore and subjected to ionizingradiation to alter the set modifier. The altered set modifier acts toincrease the mechanical strength of the sealant composition.

The sealant composition can have one or more components selected fromthe group consisting of sealants, resins, cements, settable drillingmuds, conformance fluids, and combinations thereof. The set modifier caninclude one or more components selected from an accelerator, anoxidizing agent, a set retarder or combinations thereof and can includea polymeric component. The ionizing radiation can cause the degradationof the polymeric component. The polymeric component can form anencapsulating layer over particles of the set modifier. The polymericcomponent can be mixed with the set modifier so the polymeric componentacts as a binder and the resulting mixture can then be formed into apellet. The polymeric component can form an encapsulating layer over thepellet.

The polymeric component can have a radiation tolerance of less thanabout 500 KiloGrays and can be selected from the group consisting ofpolyisobutylene, fluoroelastomers, silicon rubber, polyesters,polytetrafluoroethylene, polyacetals, polypropylene, copolymers ofpolypropylene-ethylene, polymethylpentene, polymethylmethacrylate,fluorinated ethylene propylene, and combinations thereof.

The set modifier can include an accelerator in an amount of from about0.1% to about 20% by weight of the sealant composition. Subjecting thesealant composition to the ionizing radiation can enable the acceleratorto react with compounds within the sealant composition to increase themechanical strength of the sealant composition.

The set modifier can also include an oxidizing agent in and amount ofabout 0.05% to about 5% by weight of the sealant composition capable ofattacking any set retarder present. Subjecting the sealant compositionto the ionizing radiation can enable the release of the oxidizing agentwhich reduces the retarding capability of the retarder, allowing set.

The set modifier can include a set retarder in an amount from about 0.1%to about 10% by weight of the sealant composition. The set modifier canbe a sensitized retarder, and can be a boronated compound. The ionizingradiation can be sufficient to degrade the set retarder, thus reducingthe retarding effect.

The method can further include at least one sensitizer material toincrease the sealant composition capture efficiency of the ionizingradiation. The sensitizer material can be a boron compound. The sealantcomposition can further include at least one scintillator materialcapable of emitting secondary radiation upon exposure to the ionizingradiation. The sensitizer material can also be a scintillator material.

The ionizing radiation can be selected from the group consisting ofalpha rays, beta rays, gamma rays, neutron rays, proton rays, UV raysand X-rays. The ionizing radiation can be emitted from a high-fluxneutron source that can be selected from the group consisting ofplutonium-beryllium, americium-beryllium, and americium-lithium. Thehigh flux neutron source can be an accelerator based neutron generator.

A radiation emitter can be lowered into the wellbore and the ionizingradiation can be emitted from a radiation emitter that is subject to thecontrol of technicians. Two or more radiation emitters can optionally beseparately lowered to two or more depths of the wellbore, such that thetwo or more depths of the wellbore can be subject to ionizing radiationsimultaneously.

An alternate embodiment is a method of cementing a wellbore thatincludes preparing a cement composition including hydraulic cement andsufficient water to form a slurry, adding an accelerator to the slurry,placing the slurry containing the accelerator into a wellbore, andsubjecting the slurry to ionizing radiation after the slurry is pumpedinto the wellbore to activate the accelerator. The accelerator can be acalcium salt. The accelerator can be combined with a polymericcomponent, such as mixed wherein the polymeric component acts as abinder and the resulting mixture is then formed into a pellet. Theionizing radiation can cause the degradation of the polymeric componentand facilitate the release of the accelerator. The accelerator can beadded in an amount of from about 0.1% to about 20% by weight of cement.The polymeric component can have an ionizing radiation tolerance of lessthan about 500 KiloGrays. The ionizing radiation can be emitted from ahigh-flux neutron source.

An alternate embodiment is a method of cementing a wellbore thatincludes preparing a cement composition having an accelerating agent,wherein the accelerating agent is encapsulated by a polymer, placing thecement composition into the wellbore and subjecting the placed cementcomposition to ionizing radiation. The polymer serves to isolate theaccelerating agent from the cement composition. The step of introducingthe ionizing radiation is sufficient to induce the degradation of thepolymer, thus dispersing the encapsulated accelerating agent into thecement composition.

An alternate embodiment is a method of cementing a wellbore thatincludes preparing a cement composition having an oxidizing agent and aretarder, wherein the oxidizing agent is encapsulated by a polymer butthe retarder is not, placing the cement composition into the wellboreand subjecting the placed cement composition to the ionizing radiation.The polymer serves to isolate the oxidizing agent from the cementcomposition and retarder contained therein. The step of introducing theionizing radiation is sufficient to induce the degradation of thepolymer, thus dispersing the encapsulated oxidizing agent into thecement composition and subsequently degrading the retarder, thusallowing set.

Also disclosed herein is a method of cementing a wellbore that includespreparing a cement composition with a retarder. The cement compositionis placed into a wellbore and the placed cement composition is subjectedto ionizing radiation resulting from a neutron source. The radiationthat is introduced into the cement composition is of sufficient strengthto selectively alter or degrade the molecules of the retarder, thusallowing the curing reactions in the cement to proceed. In an embodimentthe retarder is a sensitized retarder, such as a boronated retarder.

Additionally disclosed herein is a method of cementing a wellbore thatincludes preparing a cement composition including an accelerating agentand a retarder, placing the resulting cement composition into a wellboreand subjecting the placed cement composition to ionizing radiation thatis of sufficient strength to selectively alter or degrade the moleculesof the retarder, thus allowing the accelerating agent to take effectresulting in the rapid curing of the cement mixture. In an optionalembodiment, the method includes preparing a cement mixture by firstadding a sensitized retarder to a composition including cement andwater, followed by adding an accelerating agent to the compositionincluding cement, water and a sensitized retarder. In an alternativeembodiment, the accelerating agent is encapsulated by a polymer capsule,which serves to isolate the accelerating agent from the cementcomposition. The step of introducing the ionizing radiation may besufficient to induce the degradation of the polymer capsule, thusdispersing the encapsulated accelerating agent into the cementcomposition.

The preceding has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention may be more fully understood. The featuresand technical advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the detaileddescription of the embodiments of the invention, which follows.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a cross sectional side view of a wellbore.

FIG. 2 is a graph of polymer embrittlement due to neutron irradiationfor films of various materials and thickness.

FIG. 3 is a graph of gas permeance for two polymer films of differingthickness upon exposure to neutron irradiation.

FIG. 4 is a graph of conductivity illustrating the delayed release of anencapsulated material upon exposure to neutron irradiation.

DETAILED DESCRIPTION

The present invention relates to generally to wellbore operationsinvolving fluids or slurries, and more particularly, to fluids orslurries that contain accelerating agents and/or retarders that can bereleased, activated and/or deactivated on command to provide thickeningto the fluid or slurry. The fluids or slurries referred to herein can beany suitable for wellbore operations, drilling, completion, workover orproduction operations such as cements, drilling muds, lost circulationfluids, fracturing fluids, conformance fluids, sealants, resins, etc.One embodiment of the present invention relates to wellbore cementingoperations, and more particularly, to methods of cementing in wellboresusing cementitious compositions that contain accelerating agents and/orretarders that can be released and/or deactivated on command.

The cementitious compositions disclosed herein generally include waterand a cement component such as hydraulic cement, which can includecalcium, aluminum, silicon, oxygen, and/or sulfur that sets and hardensby reaction with the water.

Referring to FIG. 1, a cross sectional side view of an embodiment of awellbore 2 is illustrated. Surface casing 4, having a wellhead 6attached, is installed in the wellbore 2. Casing 8 is suspended from thewellhead 6 to the bottom of the wellbore 2. An annulus 10 is definedbetween casing 8 and the wellbore 2. Annulus flow line 12 fluidlycommunicates with annulus 10 through the wellhead 6 and/or surfacingcasing 4 with an annulus valve 14. Flow line 16 is connected to thewellhead 6 to allow fluid communication with the inner diameter ofcasing 8 and a casing valve 18. At the lower most end of casing 8 thecasing is open to the wellbore 2 or has circulation ports in the wallsof casing 8 (not shown) to allow fluid communication between the annulus10 and the inner diameter of casing 8.

A cement composition can be pumped down the casing 8 and circulated upthe annulus 10 while fluid returns are taken from the annulus 10 outflow line 12, in a typical circulation direction. Alternately the cementcomposition can be pumped into the annulus 10 from annulus flow line 12while fluid returns are taken from the inner diameter of casing 8through flow line 16. Thus, fluid flows through wellbore 2 in a reversecirculation direction.

In an alternate method a fluid composition, such as a cement slurry, canbe placed within the wellbore 2 and a sealed or filled tubular, such ascasing 8, can be lowered into the wellbore 2 such that the fluidcomposition is displaced into the annulus 10 area, thereby placing thefluid composition within the annulus 10 without pumping the fluidcomposition into the annulus 10. The above method can be referred to aspuddle cementing. The fluid composition can be a drilling fluid placedwithin the wellbore after drilling operations are complete.

Any cement suitable for use in subterranean applications may be suitablefor use in the present invention. In certain embodiments, the cementcompositions used in the present invention include hydraulic cement.Examples of hydraulic cements include but are not limited to Portlandcements (e.g., Classes A, C, G, and H Portland cements), pozzolanacements, gypsum cements, phosphate cements, high alumina contentcements, silica cements, high alkalinity cements, and combinationsthereof. Cements including shale, cement kiln dust or blast furnace slagalso may be suitable for use in the present invention. In certainembodiments, the shale may include vitrified shale; in certain otherembodiments, the shale may include raw shale (e.g., unfired shale), or amixture of raw shale and vitrified shale.

The cementitious compositions used in the present invention generallyinclude a base fluid. A wide variety of base fluids may be suitable foruse with the present invention, including, inter alia, an aqueous-basedbase fluid, a nonaqueous-based base fluid, and mixtures thereof. Wherethe base fluid is aqueous-based, it may include water that may be fromany source, provided that the water does not contain an excess ofcompounds (e.g., dissolved organics, such as tannins) that may adverselyaffect other compounds in the cement compositions. For example, a cementcomposition useful with the present invention can include fresh water,salt water (e.g., water containing one or more salts dissolved therein),brine (e.g., saturated salt water), or seawater. Where the base fluid isnonaqueous-based, the base fluid may include any number of organicliquids. Examples of suitable organic liquids include, but are notlimited to, mineral oils, synthetic oils, esters, and the like. Incertain embodiments of the present invention wherein primary cementingis performed, an aqueous-based base-fluid may be used. The base fluidmay be present in an amount sufficient to form a pumpable slurry. Moreparticularly, in certain embodiments wherein the base fluid is water,the base fluid may be present in the cement compositions used in thepresent invention in an amount in the range of from about 25% to about150% by weight of cement (“bwoc”). In certain embodiments wherein thebase fluid is water, the base fluid may be present in the cementcompositions in the range of from about 30% to about 75% bwoc. In stillother embodiments wherein the base fluid is water, the base fluid may bepresent in the cement compositions in the range of from about 40% toabout 60% bwoc. In still other embodiments wherein the base fluid iswater, the base fluid may be present in the cement compositions in therange of from about 35% to about 50% bwoc. The cement composition mayinclude a sufficient amount of water to form a pumpable cementitiousslurry. The water may be fresh water or salt water, e.g., an unsaturatedaqueous salt solution or a saturated aqueous salt solution such as brineor seawater.

Optionally, the fluid or slurry compositions used in the presentinvention may include a fluid loss control additive. A variety of fluidloss control additives may be suitable for use with the presentinvention, including, inter alia, fibers, flakes, particulates, modifiedguars, latexes, and acrylamide methyl sulfonic acid copolymers such asthose that are further described in U.S. Pat. Nos. 4,015,991; 4,515,635;4,555,269; 4,676,317; 4,703,801; 5,339,903; and 6,268,406, the entiredisclosures of which are hereby incorporated herein by reference.Generally, the fluid loss control additive is present in the cementcompositions used in the present invention in an amount sufficient toprovide a desired degree of fluid loss control. More particularly, thefluid loss control additive may be present in the cement compositionsused in the present invention in an amount in the range of from about0.1% to about 10% bwoc. In certain embodiments, the fluid loss controladditive is present in the cement compositions used in the presentinvention in an amount in the range of from about 0.2% to about 3% bwoc.

Optionally, the compositions used in the present invention also mayinclude a mechanical-property modifier. Examples of suitablemechanical-property modifiers may include, inter alia, gases that areadded at the surface (e.g., nitrogen), gas-generating additives that maygenerate a gas in situ at a desired time (e.g., aluminum powder orazodicarbonamide), hollow microspheres, elastomers (e.g., elasticparticles including a styrene/divinylbenzene copolymer), high aspectratio materials (including, inter alia, fibers), resilient graphiticmaterials, vapor/fluid-filled beads, matrix-sorbable materials havingtime-dependent sorption (initiated by, e.g., degradation), mixturesthereof (e.g., mixtures of microspheres and gases), or the like. Incertain embodiments of the present invention, the optionalmechanical-property modifier may include a latex.

In certain optional embodiments wherein microspheres are added to afluid or slurry, such as cement compositions useful with the presentinvention, the microspheres may be present in the cement compositions inan amount in the range of from about 5% to about 75% bwoc. In certainembodiments of the present invention, the inclusion of microspheres inthe cement compositions useful with the present invention may reduce thedensity of the cement composition.

In certain optional embodiments wherein one or more gas-generatingadditives are used as mechanical property modifiers in the fluid orslurry compositions used in the present invention, the one or moregas-generating additives may include, inter alia, aluminum powder thatmay generate hydrogen gas in situ, or they may include azodicarbonamidethat may generate nitrogen gas in situ. Other gases and/orgas-generating additives also may be suitable for inclusion in the fluidor slurry compositions used in the present invention. Where included, agas-generating additive may be present in cement compositions in anamount in the range of from about 0.1% to about 5% bwoc. In certainembodiments where the gas-generating additive is aluminum powder, thealuminum powder may be present in the cement compositions in an amountin the range of from about 0.1% to about 1% bwoc. In certain embodimentswhere the gas-generating additive is an azodicarbonamide, theazodicarbonamide may be present in the cement compositions in an amountin the range of from about 0.5% to about 5% bwoc.

Optionally, the fluid or slurry compositions used in the presentinvention also may include additional suitable additives, includingdefoaming agents, dispersants, density-reducing additives, surfactants,weighting materials, viscosifiers, fly ash, silica, free water controlagents, and the like. Any suitable additive may be incorporated withinthe fluid or slurry compositions used in the present invention.

The fluid or slurry compositions used in the present invention canfurther include a set retarder. Set retarding admixtures lengthen thetime at which the fluid or slurry composition remains a fluid. Theseretarding admixtures consequently allow a fluid or slurry, such ascement, to be pumped along long distances without the effect ofpremature setting. A broad variety of set retarders may be suitable foruse in the fluid or slurry compositions used in the present invention.For example, the set retarder may include, inter alia, phosphonic acid,phosphonic acid derivatives, lignosulfonates, salts, sugars,carbohydrate compounds, organic acids, carboxymethylatedhydroxyethylated celluloses, synthetic co- or ter-polymers includingsulfonate and carboxylic acid groups, and/or borate compounds. Incertain embodiments, the set retarders used in the present invention arephosphonic acid derivatives, such as those described in U.S. Pat. No.4,676,832, the entire disclosure of which is hereby incorporated herein.Examples of suitable borate compounds include, but are not limited to,sodium tetraborate and potassium pentaborate. Examples of suitableorganic acids include, inter alia, gluconic acid and tartaric acid.Generally, the set retarder is present in the fluid or slurrycompositions used in the present invention in an amount sufficient todelay the setting of the fluid or slurry composition in a subterraneanformation for a desired time. More particularly, the set retarder may bepresent in the fluid or slurry compositions used in the presentinvention in an amount in the range of from about 0.1% to about 10%bwoc. In certain embodiments, the set retarder is present in the fluidor slurry compositions used in the present invention in an amount in therange of from about 0.5% to about 4% bwoc.

The set retarders of the current invention may include asensitizer-containing retarder, such as a boron-containing retarder. Thesensitizer can be made from a material having a strong radiationabsorption property. The sensitizer can also be a scintillator material.The sensitizer can be any material that increases the capture efficiencyof the ionizing radiation within the slurry. This sensitizer-containingretarder, also referred to as a sensitized retarder, can be aboron-containing retarder, also referred to as a boronated retarder, mayinclude a wide variety of set retarders, including the set retardersdisclosed herein, wherein the selected set retarder, or combination orset retarders, additionally includes at least one boron atom. Asdiscussed in the immediately preceding paragraph, sugars and/orcarbohydrates can be used as a retarder in the setting of a cementcomposition. In an embodiment, the retarder is a sensitized sugar orcarbohydrate. In a more specific embodiment, the sensitized retarder isboronated glucose. In an even more specific embodiment, the boronatedglucose is represented by 3-O-(o-Carborany-1-ylmethyl)-D-glucose, aspresented in U.S. Pat. No. 5,466,679, to Soloway et al.

Various elements can be utilized as a sensitized material. In general,elements having a greater absorption cross-section than the wellboretreatment fluid composition can be used to increase the captureefficiency of the ionizing radiation within the composition. Manywellbore treatment fluid compositions can comprise calcium, which has anabsorption cross-section for 2200 m/s neutrons of about 0.43 barn. Anon-limiting listing of elements having an absorption cross-section for2200 m/s neutrons of 10 barn or greater is shown below in Table 2. Abarn is defined as being 10⁻²⁸ m², and corresponds to approximately thecross sectional area of a uranium nucleus.

TABLE 2 Absorption cross section for 2200 m/s neutrons Absorption crosssection for 2200 m/s neutrons Element (barn) Li 71 B 767 Cl 34 Sc 28 Mn13 Co 37 Se 12 Kr 25 Tc 20 Rh 145 Ag 63 Cd 2,520 In 194 Xe 24 Pr 12 Nd51 Pm 168 Sm 5,922 Eu 4,530 Gd 49,700 Tb 23 Dy 994 Ho 65 Er 159 Tm 100Yb 35 Lu 74 Hf 104 Ta 21 W 18 Re 90 Os 16 Ir 425 Pt 10 Au 99 Hg 372

The compositions of the present invention may also include anaccelerator. The accelerator aids in overcoming possible delays causedby the set retarders by shortening the setting time of the fluid orslurry composition. A broad variety of accelerators may be suitable foruse in the fluid or slurry compositions used in the present invention,the accelerator may include any component that reduces the setting timeof a cement composition. For example, the accelerator may include alkaliand alkali earth metal salts, silicate salts, aluminates and amines,such as triethanolamine. In an embodiment, the accelerator is a calciumsalt. The calcium salt may be selected from the group consisting ofcalcium formate, calcium nitrate, calcium nitrite and calcium chloride.In a specific embodiment, the accelerator is calcium chloride. Theaccelerator may be present in the fluid or slurry compositions used inthe present invention in an amount in the range of from about 0.1% toabout 20% bwoc. In certain embodiments, the accelerator is present inthe cement compositions used in the present invention in an amount inthe range of from about 4% to about 12% bwoc.

The accelerators of the current invention may be combined with apolymeric component. In an embodiment the accelerator is encapsulated bythe polymeric component. In another aspect, the accelerator is uniformlymixed with the polymeric, which acts as a binder, the resulting mixtureis then pressed into a pellet. In yet another aspect, the resultingpellet is ultimately encapsulated by a polymeric component. Thepolymeric component used as a binder in forming the pellet may be of adifferent composition from the polymeric component used in encapsulatingthe pellet. Further, it may be of a composition sensitive to alkalinehydrolysis, such that the alkaline environment of the cement systemcontributes to its more rapid degradation. The encapsulating polymerlayer can be applied using a polymer coating method selected from thegroup consisting of dip coating, spray coating, extrusion coating,transfer printing and any combination thereof. The encapsulating polymerlayer may also be applied using any common polymer coating method.

The oxidizing agents of the current invention may be combined with oneor more polymeric components. They may be present in an amount of about0.05% to about 5% of the fluid or slurry composition, and capable ofattacking any set retarder present. In an embodiment the oxidizer isencapsulated by the polymeric component. In another aspect, the oxidizeris uniformly mixed with the polymeric, which acts as a binder, theresulting mixture is then pressed into a pellet. In yet another aspect,the resulting pellet is ultimately encapsulated by a polymericcomponent. The polymeric component used as a binder in forming thepellet may be of a different composition from the polymeric componentused in encapsulating the pellet and may be selected from polymerespecially resistant to oxidation. Subjecting the fluid or slurrycomposition to the ionizing radiation can enable the release of theoxidizing agent which reduces the retarding capability of the retarder,allowing set.

In an embodiment the polymeric component selected in the presentinvention is durable in the high alkaline environment found in cementand exhibits a low tolerance to radiation. In more specific embodiments,the polymeric component exhibits a radiation tolerance of less thanabout 500 KiloGrays, optionally less than about 250 KiloGrays,optionally less than about 100 KiloGrays. Alternatively, the polymericcomponent has a radiation tolerance of from about 4 to about 65KiloGrays. A non-limiting listing of polymer degradation upon exposureto ionizing radiation is given in Table 1.

TABLE 1 Polymer Tolerance (kGy) Teflon 5 Polyacetals 15Propylene-ethylene copolymers 25-60 Aliphatic Nylons 50 Polystyrene10,000 Phenolics 50,000

In an aspect, the polymeric component is selected from the groupconsisting of polyisobutylene, fluoroelastomers, silicon rubber,polyesters, polytetrafluoroethylene (PTFE) (available under the tradename TEFLON® from E.I. du Pont de Nemours and Company), polyacetals(available under the trade name DELRIN® from E.I. du Pont de Nemours andCompany and under the trade name CELCONO from Ticona), polypropylene,copolymers of polypropylene-ethylene, polymethylpentene, fluorinatedethylene-propylene, perfluoroalkoxy (PFA), polymethylmethacrylate (PMMA)and combinations thereof.

Referring to FIGS. 2 and 3, various polymer films were exposed to aneutron flux of 1.2×10¹³/s and tested for embrittlement and gaspermeability over time. The film material and thickness were PMMA at 50microns; Delrin at 75 microns; PFA at 25 and 12.5 microns; and PTFE at 5microns. FIG. 2 illustrates that PMMA with a thickness of 50 micronsshows embrittlement effect at about 18 minutes and at about 50 minutesthe film had degraded to a degree that it could no longer be tested. Itis also seen that some materials such as Delrin are more susceptible toradiation degradation than other materials such as PMMA or PFA. TheDelrin film with a thickness of 75 microns degrades before the PFAhaving a thickness of 12.5 microns.

FIG. 3 illustrates the effect of film thickness on gas permeability andthat the PFA film of 25 microns thickness retains gas impermeability forabout twice as long as a PFA film of 12.5 microns thickness exposed tothe same radiation. FIG. 3 also illustrates that both PFA films observedgas permeability at a time earlier than the embrittlement effect wasobserved as shown in FIG. 2.

Referring to FIG. 4, a sample of sodium metasilicate, available asEconolite from Halliburton, was coated with a layer of FluoroPel™ PFAand with a layer of FluoroPel™ PFA with B₄C. The sample was exposed to aneutron flux of 1.2×10¹³/s and tested for conductivity over time. FIG. 4shows that the coating provided a delayed release profile of the sodiummetasilicate that is relative to the radiation exposure. FluoroPel™ isavailable from Cytonix corporation.

In a further example a sample of Uranine dye on a glass slide wasencapsulated using FluoroPel™ PFA with a thickness of approximately 36microns in a container of fluid. The encapsulated dye was exposed to aneutron flux of 1.2×10¹³/s for 50 minutes, during which the Uranine dyehad visibly colored the fluid, indicating its dissipation into thefluid.

The polymeric component may also contain an additional material topromote the degradation of the polymer and/or the release of theaccelerator into the fluid or slurry. In an embodiment, a promoter forfree-radical chain scissioning is added to the polymer capsule and/orthe polymeric component used as a binder to accelerate the polymerdegradation once triggered by exposure to the ionizing radiation. In afurther embodiment, the polymeric component may also contain asensitizer made from a material having a strong radiation absorptionproperty. The promoter or sensitizer can be any material that increasesthe capture efficiency of the ionizing radiation within the slurry. Inembodiments the promoter or sensitizer material is a boron compound. Inembodiments the promoter or sensitizer material has an ionizingradiation tolerance of less than 500 KiloGrays.

Methods of this invention for isolating a portion of a wellbore mayinclude forming a sealant composition including a set modifier, pumpingthe sealant composition containing the set modifier into a wellbore, andsubjecting the sealant composition to ionizing radiation after placementinto the wellbore. The set modifier of the invention may be combinedwith a polymeric component. The polymeric component can serve to preventthe release of the set modifier, such as an accelerator, into thesealant composition. The ionizing radiation introduced is sufficient todissolve, degrade, or otherwise break down, the polymeric component thusallowing the set modifier to be released into the sealant composition.Once the set modifier is released, it is dispersed into and reacts withthe sealant composition, resulting in the initiation of the settingprocess. The release of the ionizing radiation, which is under thecontrol of technicians in the field, thus acts as a trigger ininitiating the setting of the sealant composition.

The polymeric component may be combined with the set modifier by meansof encapsulation, binding with the set modifier in a mixture, or both.The polymer coating used in the methods of this invention may be anypolymeric component that will degrade upon being subjected to ionizingradiation. In an embodiment, the polymeric component will degrade fromexposure to gamma radiation. In another embodiment, the polymericcomponent will degrade from exposure to gamma radiation in levels ofless than about 500 KiloGrays. In yet another embodiment, the polymerwill degrade from the ionizing radiation emitted from a gamma raygenerator that is also used on oil well logging instruments.

The type and level of ionizing radiation used in the methods of thisinvention may depend upon the polymeric component(s) that are combinedwith the accelerator. The type and level of the ionizing radiation maybe dependent upon what is capable of degrading the polymer component(s).In an embodiment, the type of ionizing radiation includes alpha rays,beta rays, gamma rays, neutron rays, proton rays, UV rays and X-rays, orcombinations thereof. In an optional embodiment, the amount of ionizingradiation required to degrade the polymeric component(s) is less thanabout 500 KiloGrays.

Methods of this invention for isolating a wellbore may include forming asealant composition including a set modifier, pumping the sealantcomposition containing the set modifier into a wellbore and subjectingthe sealant composition to ionizing radiation after placement into thewellbore. The set modifier of the invention may be a retarder,optionally a sensitized retarder, such as a boronated retarder. Thesensitized retarder of the invention is susceptible to certain types ofionizing radiation. The ionizing radiation introduced is sufficient todissolve, or otherwise break down, the retarder thus allowing thesetting of the sealant composition to proceed.

The types and level of the ionizing radiation used in the methods ofthis invention may depend upon the type of sensitized retarder used. Thetypes and level of the ionizing radiation used may be dependent uponwhat is capable of altering or destroying the molecules of thesensitized retarder. In an embodiment, the ionizing radiation source isa high-flux neutron source. In more specific embodiment, the high-fluxneutron source is selected from the group consisting ofplutonium-beryllium, americium-beryllium, and americium-lithium.Optionally, the high flux neutron source is an accelerator based neutrongenerator. In an embodiment, the type of ionizing radiation includes oneor more of: alpha rays, beta rays, gamma rays, neutron rays, protonrays, UV rays, X-rays, or combinations thereof. In an optionalembodiment, the amount of ionizing radiation required to alter ordestroy the molecules of the sensitized retarder is less than about 500KiloGrays.

Methods of this invention for isolating a wellbore may include forming asealant composition that includes both an accelerator or oxidizing agentand a retarder, and exposing the sealant composition to ionizingradiation. The accelerator or oxidizing agent can be released oractivated by exposure of the sealant composition to the ionizingradiation, thus able to accelerate the setting of the sealantcomposition. The retarder can be altered upon exposure of the sealantcomposition to radiation, thus its ability to retard the setting of thesealant composition can be hindered.

Methods of this invention for cementing a wellbore may include the stepsof forming a cement composition including hydraulic cement and asufficient amount of water to form a slurry, adding to the slurry adesired amount of an accelerator or oxidizing agent, pumping the slurrycontaining the accelerator or oxidizing agent into a wellbore, andsubjecting the slurry to ionizing radiation after placement of theslurry into the wellbore. The accelerator or oxidizing agent of theinvention may be combined with a polymeric component. The polymericcomponent serves to prevent the release of the accelerator or oxidizingagent into the cement slurry. The ionizing radiation introduced issufficient to dissolve, degrade, or otherwise break down, the polymericcomponent thus allowing the accelerator or oxidizing agent to bereleased into the cement slurry. Once the accelerator or oxidizing agentis released, it is dispersed into the cement slurry and reacts with theslurry or the retarder, resulting in the initiation of the settingprocess. The release of the ionizing radiation, which is under thecontrol of technicians in the field, thus acts as a trigger ininitiating the setting of the cement slurry.

The polymeric component may be combined with the accelerator oroxidizing agent by means of encapsulation, binding with the acceleratorin a mixture, or both. The polymer coating used in the methods of thisinvention may be any polymeric component that will degrade upon beingsubjected to the ionizing radiation. In an embodiment, the polymericcomponent will degrade from exposure to gamma radiation. In anotherembodiment, the polymeric component will degrade from exposure to gammaradiation in levels of less than about 500 KiloGrays. In yet anotherembodiment, the polymer will degrade from ionizing radiation emittedfrom a gamma ray generator that is also used on oil well logginginstruments.

The type and level of ionizing radiation used in the methods of thisinvention may depend upon the polymeric component(s) that are combinedwith the accelerator or oxidizing agent. The type and level of theionizing radiation may be dependent upon what is capable of degradingthe polymer component(s). In an embodiment, the type of ionizingradiation includes alpha rays, beta rays, gamma rays, X-rays, orcombinations thereof. In an optional embodiment, the amount of ionizingradiation required to degrade the polymeric component(s) is less thanabout 500 KiloGrays.

Methods of this invention for cementing a wellbore may include the stepsof forming a cement composition including hydraulic cement and asufficient amount of water to form a slurry, adding to the slurry adesired amount of a retarder, pumping the slurry containing the retarderinto a wellbore, and subjecting the slurry to ionizing radiation afterplacement of the slurry into the wellbore. The retarder of the inventionmay be a sensitized retarder as disclosed herein, such as a boronatedretarder. The sensitized retarder of the invention is susceptible tocertain types of irradiation. The ionizing radiation introduced issufficient to dissolve, or otherwise break down, the retarder thusallowing the setting of the cement slurry to proceed.

The types and level of radiation used in the methods of this inventionmay depend upon the type of sensitized retarder used. The types andlevel of ionizing radiation used may be dependent upon what is capableof altering or destroying the molecules of the sensitized retarder. Inan embodiment, the ionizing radiation source is a high-flux neutronsource. In more specific embodiment, the high-flux neutron source isselected from the group consisting of plutonium-beryllium,americium-beryllium, and americium-lithium. Optionally, the high fluxneutron source is an accelerator based neutron generator. In anembodiment, the type of ionizing radiation includes alpha rays, betarays, gamma rays, X-rays, or combinations thereof. In an optionalembodiment, the amount of ionizing radiation required to alter ordestroy the molecules of the sensitized retarder is less than about 500KiloGrays. In embodiments the sensitizer can also be a scintillatormaterial.

Methods of this invention for cementing a wellbore may include the stepsof forming a cement composition including hydraulic cement and asufficient amount of water to form a slurry, adding to the slurry adesired amount of a set retarder, either conventional or sensitized andan accelerator or oxidizing agent, pumping the slurry containing theretarder and the accelerator into a wellbore, and subjecting the slurryto ionizing radiation after placement of the slurry into the wellbore.The accelerator or oxidizing agent of the invention may be combined witha polymeric component. The polymeric component serves to prevent therelease of the accelerator or oxidizing agent into the cement slurry.The ionizing radiation introduced is sufficient to dissolve, degrade, orotherwise break down, the polymeric component thus allowing theaccelerator to be released into the cement slurry. Once the acceleratoror oxidizing agent is released, it can disperse into the cement slurryand react with the slurry or the retarder, resulting in the initiationof the setting process. The sensitized retarder of the invention issusceptible to certain types of irradiation. The ionizing radiationintroduced is sufficient to dissolve, or otherwise break down, theretarder thus allowing the setting of the cement slurry to proceed. Therelease of the ionizing radiation, which is under the control oftechnicians in the field, thus acts as a trigger in initiating thesetting of the cement slurry by releasing the accelerator andsufficiently altering or destroying the retarder.

The type and level of the ionizing radiation delivered to thecementitious slurry may depend on the method used. In methods wherein anaccelerator is added and a set retarder is not added, the irradiationshould be capable of breaking down the polymeric compound(s)sufficiently to release or otherwise activate the accelerator. Inmethods wherein an accelerator is not added and a set retarder is added,the ionizing radiation should be capable of altering or destroying theretarder. In some embodiments, wherein an accelerator or oxidizing agentand a set retarder are added to the cement slurry, the ionizingradiation simultaneously breaks down the polymeric compound(s) anddestroys the retarder. In other embodiments wherein an accelerator oroxidizing agent and a set retarder are added to the cement slurry, afirst ionizing radiation source is capable of destroying the retarderand a second ionizing radiation source is capable of breaking down thepolymeric compound(s). The first and second ionizing radiation sourcemay be delivered simultaneously. Alternatively, the ionizing radiationsource capable of breaking down the polymeric component can be deliveredfirst, followed by the ionizing radiation source capable of destroyingthe retarder. Alternatively, the ionizing radiation source capable ofdestroying the retarder can be delivered first, followed by the ionizingradiation source capable of breaking down the polymeric component.

In an embodiment, the set retarder and/or the accelerator or oxidizingagent are/is added to the cement mixture before water is added to themixture. In another embodiment, the set retarder and/or the acceleratoror oxidizing agent are/is added to the cement mixture after water hasbeen added to the mixture. In yet another embodiment, set retarder isadded before the accelerator or oxidizing agent. In yet anotherembodiment, the accelerator is added before the set retarder. In afurther embodiment, the accelerator and/or set retarder is/are addedduring the mixing of the cement and water.

In an embodiment, once the cementitious composition containing the setretarder and/or accelerating agent or oxidizing agent is obtained, theslurry is then placed in the wellbore, such as in a wellbore/casingannulus. Upon the placement of the slurry containing the set retarderand/or accelerating agent or oxidizing agent in the wellbore, the cementparticles and the set retarder and/or accelerating agent or oxidizingagent should be substantially uniformly mixed with the cement particlesin the cement slurry.

In a further embodiment, a set retarder as well as both an acceleratorand oxidizer are added to the fluid or slurry. Upon being exposed to theionizing radiation both the accelerator and oxidizer are released. Thesimultaneous destruction of the retarder by the oxidizer and theacceleration of cement hydration by the accelerator provide rapid set.

According to embodiments of the invention, after the slurry is placed inthe wellbore, the ionizing radiation is introduced. Ionizing radiationcontains subatomic particles or electromagnetic waves that are energeticenough to detach electrons from atoms or molecules, thereby ionizingthem. The occurrence of ionization depends on the energy of theintruding individual particles or waves. An intense flood of particlesor waves may not cause ionization if these particles or waves do notcarry enough energy to be ionizing. In an embodiment, the amount of theionizing radiation introduced into the wellbore is determined by theamount of ionizing radiation required to sufficiently alter thepolymeric component to enable release of at least a portion of theaccelerator or oxidizing agent. In another embodiment, the amount of theionizing radiation introduced into the wellbore is determined by theamount of ionizing radiation required to sufficiently destroy at least aportion of the retarder. The ionizing radiation can be emitted fromcharged particles. In an embodiment, the charged particles include alphaparticles, beta particles, or gamma particles, or combinations thereof.

In an embodiment, the ionizing radiation is introduced by an ionizingradiation emitter located at a point within the wellbore. In anotherembodiment, an ionizing radiation emitter located at the surfaceintroduces the ionizing radiation directed downward into the wellbore.In another embodiment, a radiation source is lowered into the wellbore,such as on a wireline, and the ionizing radiation is emitted. Theradiation source can be shielded to not emit the ionizing radiationother than when the shielding is removed. For example a radiation sourcecan be shielded at the surface when personnel could otherwise beexposed. Once the ionizing radiation source is placed in the wellboreand radiation can safely be emitted, the shield can be removed oropened, such as by an electronically activated signal transmitted fromthe surface down the wireline to the shield. In an embodiment theradiation emitter can emit ionizing radiation as it is lowered down thewellbore and as it is pulled up the length of the wellbore. In a furtherembodiment, two or more ionizing radiation emitters are separatelylowered to two or more depths, such that two or more depths of thewellbore may be subject to the ionizing radiation simultaneously.

In an embodiment, the ionizing radiation is introduced under the controlof a technician in the field. The technician, engineer, or other on-siteemployee, can have the control over the emission of the ionizingradiation by imputing a signal that causes a release of the ionizingradiation from an emitter. In this embodiment, the ionizing radiation isreleased on demand from the technician in the field. The ionizingradiation can be released by a control system having parameters such astimer, flow meter, temperature sensor, or the like. In anotherembodiment, the lowering and/or emitting of the ionizing radiationsource is triggered by a timing mechanism. In a further embodiment, thelowering and/or emitting of the radiation source is triggered by a flowmeter that detects the amount of the cement mixture delivered into thewellbore.

As mentioned above, the ionizing radiation of the current invention canbe under the control of technicians in the field. The release of theionizing radiation emissions act as a trigger in the sense that theradiation can destroy the sensitized retarder, thus allowing the settingof the cement slurry to proceed. The release of the ionizing radiationmay also act as a trigger when the ionizing radiation emissions act todegrade the polymeric component of the accelerator or oxidizing agent,thus releasing the accelerator or oxidizing agent, or both, into thecement slurry. Once the accelerator or oxidizing agent is released, itis dispersed into the cement slurry and reacts with the slurry orretarder, resulting in the acceleration of the setting process.Therefore, technicians in the field can trigger the thickening of thecement slurry. This triggering process puts the thickening of the cementslurry under the control of technicians in the field and can result in adecrease in the time needed to wait on cement (WOC) in the drilling andcompletion of a wellbore.

The fluid or slurry compositions used in the present invention canfurther include a scintillator material. The scintillator material canact to increase capture efficiency of the ionizing radiation and/or canemit radiation upon exposure to the ionizing radiation. A scintillatormaterial having the property of fluorescence can emit radiation, whichcan be referred to as secondary radiation, as the result of absorptionof radiation from another source. For example a scintillator materialmay emit gamma rays, X-rays, or UV radiation upon exposure to neutronsor gamma rays. This secondary radiation can be used to provide radiationto promote the degradation of the polymer and/or the release of theaccelerator into the fluid or slurry. If the secondary radiationincludes photons or particles with the same wavelength as that of theabsorbed radiation, it can be referred to as resonance radiation.

A variety of neutron scintillators are known, a non-limiting listincludes LiF/ZnS:Ag, Li-glass, and LiI:Eu. LiF/ZnS:Ag is shown toproduce a very large neutron multiplication factor and has been measuredat 160,000 photons per neutron absorbed with the majority of theemission occurring below about 450 nm. Li-glasses typically have anemission maximum below about 400 nm.

A variety of gamma ray scintillators are known, a non-limiting listincludes NaI:Tl⁺, Bi₄Ge₃O₁₂(GSO), Gd₂SiO₅:Ce³⁺, ZnS:Ag. Alkali halidesinclude CsI and NaI. Typical emission maxima observed for somescintillators are: CsI—about 300 nm; BaF₂—about 190 to about 305 nm;CaF₂:Eu—about 410 nm; GSO:Ce—about 420 nm; Yttrium AluminumPerovskite:Ce (Y:Al:CaTiO₃:Ce)—about 350 nm.

The scintillator may be used in a powder or crystal form or with acoating such as a polymer. Advantages of incorporating scintillatorsinto the fluid or slurry of the present invention can include the localcreation of ionizing secondary radiation that can minimize the impactfrom the well casing or other environmental influences. Potentiallylarge multiplication factors are possible, for example somescintillators will emit more than 10,000 photons for each absorbedionizing radiation particle/photon. The photons produced byscintillators can be in the X-ray and UV spectral regions that can behighly absorbed by the polymeric component of the slurry. Since thesephotons are created locally by the scintillation their emission mayincrease the efficiency of the polymer encapsulation degradation. Morephotons above the scission threshold can increase the rate of thepolymer degradation that can speed the thickening of the cement slurryand enhance the set-on-command behavior.

The scintillator material may be added to the fluid or slurry. Thescintillator material may be incorporated into a polymeric componentthat forms an encapsulating layer over particles of an accelerator. Thescintillator material may be added to a polymeric component that forms abinder for an accelerator that is formed into a pellet and/or apolymeric component that forms an encapsulating layer over the pellet.The scintillator material can also be a sensitizer material.

The term “cementitious composition” as may be used herein includespastes (or slurries), mortars, and grouts, such as oil well cementinggrouts, shotcrete, and concrete compositions including a hydrauliccement binder. The terms “paste”, “mortar” and “concrete” are terms ofart: pastes are mixtures composed of a hydratable (or hydraulic) cementbinder (usually, but not exclusively, Portland cement, Masonry cement,Mortar cement, and/or gypsum, and may also include limestone, hydratedlime, fly ash, granulated blast furnace slag, and silica fume or othermaterials commonly included in such cements) and water; “mortars” arepastes additionally including fine aggregate (e.g., sand), and“concretes” are mortars additionally including coarse aggregate (e.g.,crushed rock or gravel). The cement compositions described in thisinvention are formed by mixing required amounts of certain materials,e.g., a hydraulic cement, water, and fine and/or coarse aggregate, asmay be required for making a particular cementitious composition.

The term “accelerator” can include any component, which reduces thesetting time of a cement composition. For example, the accelerator mayinclude alkali and alkali earth metal salts, such as a calcium salt. Thecalcium salt may include calcium formate, calcium nitrate, calciumnitrite or calcium chloride.

The term “encapsulating layer” as used herein can mean any form ofcoating or binding wherein most of the material being encapsulated isenclosed within the layer and that the dissipation of the material issubstantially restricted by the layer. It does not mean that all of thematerial being encapsulated is enclosed within the layer or that thematerial being encapsulated cannot leak through the encapsulating layer.

The term oxidizer can include any component which is capable ofdegrading the retarder present. These include, but are not limited toalkaline earth and zinc salts of peroxide, perphosphate, perborate,percarbonate; calcium peroxide, calcium perphosphate, calcium perborate,magnesium peroxide, magnesium perphosphate, zinc perphosphate; calciumhypochlorite, magnesium hypochlorite, chloramine T, trichloroisocyanuricacid, trichloromelamine, dichloroisocynaurate dihydrate, anhydrousdichloroisocynaurate; and mixtures thereof.

The term “radiation tolerance” as used herein is the amount of ionizingradiation that a material can withstand without noticeable or measurabledegradation.

The term “retarder” or “set retarder” can include boronated ornon-boronated forms of phosphonic acid, phosphonic acid derivatives,lignosulfonates, salts, sugars, carbohydrate compounds, organic acids,carboxymethylated hydroxyethylated celluloses, synthetic co- orter-polymers including sulfonate and carboxylic acid groups, and/orborate compounds.

The terms “ionizing radiation” or “radiation” can be referred to asionization inducing or indirectly ionizing, that are able to detachelectrons from atoms or molecules, and can include alpha rays, betarays, gamma rays, neutron radiation, proton rays, UV and X-rays.

The term “set” as used herein refers to an increase in mechanicalstrength of a fluid or slurry sufficient to perform a desired result,such as to restrict movement of an item or impede fluid flow or pressuretransfer through a fluid. A cement may be referred to as set when it canrestrict the movement of a pipe, or impede fluid flow or pressuretransfer, regardless of whether the cement has cured to a fully solidcomposition. A fluid or slurry can be referred to as set when it hasthickened to a sufficient level that it achieves the desired result,such as the isolation of a particular zone or the restriction of fluidflow or pressure transfer, regardless of whether it has reached itsfinal consistency.

Depending on the context, all references herein to the “invention” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present invention, which areincluded to enable a person of ordinary skill in the art to make and usethe inventions when the information in this patent is combined withavailable information and technology, the inventions are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the invention may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

While compositions and methods are described in terms of “comprising,”“containing,” or “including” various components or steps, thecompositions and methods can also “consist essentially of” or “consistof” the various components and steps. All numbers and ranges disclosedabove may vary by some amount. Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number and any included rangefalling within the range is specifically disclosed. In particular, everyrange of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee.

1. A method of isolating a portion of a wellbore comprising: placing asealant composition into a subterranean formation after drilling of thewellbore therein wherein the sealant composition comprises a setmodifier selected from the group consisting of an accelerator, anoxidizing agent, a set retarder, and combinations thereof; andsubjecting the sealant composition to ionizing radiation whereinsubjecting the sealant composition to the ionizing radiation alters theset modifier; wherein the sealant composition comprises a polymericcomponent. 2.-16. (canceled)
 17. The method of claim 1, wherein the setmodifier comprises a set retarder added in an amount from about 0.1% toabout 10% by weight of the sealant composition.
 18. The method of claim1, wherein the set modifier comprises an oxidizing agent added in anamount of about 0.05% to about 5% by weight of the sealant composition.19. The method of claim 1, wherein subjecting the sealant composition tothe ionizing radiation enables an oxidizing agent to degrade a retarderand reduce its retarding effect.
 20. The method of claim 1, wherein theset modifier is a sensitized retarder.
 21. The method of claim 20,wherein the sensitized retarder is a boronated compound.
 22. The methodof claim 20, wherein the ionizing radiation is sufficient to degrade andreduce the retarding effect of the set retarder. 23.-45. (canceled) 46.A method of cementing a wellbore comprising: preparing a cementcomposition comprising: hydraulic cement, sufficient water to form aslurry, and a set retarder; placing the cement composition into thewellbore; and subjecting the slurry to ionizing radiation to degrade theset retarder.
 47. The method of claim 46, wherein the set retarder is asensitized retarder.
 48. The method of claim 47, wherein the sensitizedretarder is a boronated compound.
 49. The method of claim 46, whereinthe ionizing radiation is sufficient to degrade the retarder and allowthe cement composition to set.
 50. The method of claim 46, wherein theamount of set retarder added is in an amount of from about 0.1% to about10% by weight of the cement.
 51. The method of claim 46, wherein theionizing radiation is emitted from a high-flux neutron source.
 52. Themethod of claim 51, wherein the high-flux neutron source is selectedfrom the group consisting of plutonium-beryllium, americium-beryllium,americium-lithium, and combinations thereof.
 53. The method of claim 51,wherein the high flux neutron source is an accelerator based neutrongenerator.
 54. The method of claim 46, further comprising a scintillatormaterial capable of emitting secondary ionizing radiation upon exposureto the ionizing radiation.
 55. The method of claim 54, wherein thescintillator material is selected from the group consisting ofLiF/ZnS:Ag, Li-glass, LiI:Eu, NaI:Tl⁺, Bi₄Ge₃O₁₂(GSO), Gd₂SiO₅:Ce³⁺,ZnS:Ag, CsI, NaI, BaF², CaF₂:Eu, GSO:Ce, YAI:CaTiO₃:Ce, and combinationsthereof. 56.-60. (canceled)